This study is designed to determine: 1) The mode(s) of inheritance of mitral valve prolapse and whether it is one or several phenotypically similar conditions; 2) whether, if more than one type of mitral valve prolapse exists on genetic grounds, these can be distinguished by clinical manifestations; 3) the clinical findings which predict which individuals or families are at high risk for complications; 4) the genetic linkage of mitral valve prolapse; and 5) whether an underlying biochemical abnormality can be demonstrated. Initial studies have supported an autosomal dominant mode of inheritance of most if not all cases of mitral valve prolapse, with essentially complete expression in adult females but reduced expression in children and adult males. Neither symptoms nor the presence or type of auscultatory abnormalities in probands had any impact on the proportion of relatives who manifested mitral valve prolapse. Studies in the coming year will utilize both nuclear and large extended families to assess modes of inheritance, genetic linkage and patterns of clinical manifestations in order to meet the general objectives of study. These findings will be related in selected families to biochemical findings in the mitral valve obtained at surgery or autopsy, and to clinical analyses or cardiac arrhythmias and autonomic nervous system dysfunction.